Controlling your exposure to light is crucial to fighting jet lag, as light is a trigger for your body to wake up. / Jupiterimages

by Nancy Trejos, USA TODAY

by Nancy Trejos, USA TODAY

So much so that NASA has a fatigue-management team at the Johnson Space Center in Houston trying to devise strategies to deal with it. Astronauts are constantly traveling to space agencies in Germany, Japan and Russia for training.

And when they get there, "they have to hit the ground running," says Steven Lockley, a neuroscientist specializing in sleep medicine at Harvard University who does consulting for the team. "They can't spend two weeks adapting. They need to do training."

If you've ever traveled across time zones, you've probably felt the symptoms of jet lag: fatigue, trouble sleeping, digestive problems, headaches and irritability. Business travelers who have to drop into cities for a short period of time and be productive say it's a major problem.

"Jet lag is something I learned to manage for my health, productivity and sanity," says Stephanie Hackney, who has traveled to 43 countries as a travel blogger.

Research shows that jet lag affects how people work. For three weeks, participants in a study at Boston's Brigham and Women's Hospital were placed on 28-hour days with six hours of sleep to mirror the effects of jet lag. Their work production slowed down in that time.

Jet lag isn't good for leisure travelers, either. Who wants to spend their first day in Paris feeling disoriented?

In a British Airways survey of passengers, 67% said they didn't know how to manage jet lag. The airline has developed an online "Jet Lag Advisor" with British sleep expert Chris Idzikowski. Plug in some information about your sleep patterns, and you'll get a plan for combating the disorder.

Many other doctors and companies have tried to come up with remedies for jet lag. And some hotels are trying to do more than providing softer pillows to help travelers deal with jet lag. The MGM Grand Hotel and Casino in Las Vegas, for instance, has introduced 42 "Stay Well" rooms with special lighting that is supposed to improve the body's internal clock and help regulate melatonin production.

But Lockley says there's no one quick fix. How much a person is affected by jet lag depends on several factors, such as the number of hours you're ahead or behind, the time of day you leave, and the direction you travel.

The rule of thumb is it takes about a day for each time zone you cross to adjust.

"If you're going to Moscow and have to sleep nine hours earlier, that's hard to do, and it takes about a day to equilibrate," says Smith Johnston, a flight surgeon and the chief of the fatigue management team at NASA. "You're there a week, you get in sync and now you're back."

Lockley has helped NASA develop strategies for their astronauts to fly all over the world and even beyond it. While they are tailored to each individual astronaut, Lockley says there are some principles that the average traveler can adapt to their bodies.

Your internal clock

First, Lockley says, any traveler should understand the science behind jet lag. Everyone has a circadian rhythm, or an internal clock.

Some people have shorter internal clocks and some have longer ones. Those who have shorter ones tend to sleep and wake up early. Those with longer ones stay up and wake up later.

When you travel westward, you have to delay your clock. Say you live in New York. That means people in Los Angeles are three hours delayed behind you. When you go east, you have to advance your clock. When you're just biting into dinner in Boston, people in London are off to bed.

Three-quarters of people have longer, or delayed, clocks. "That's why most people find it easier to travel westward," Lockley says. "Their body clocks are already going in that direction."

How can you use that to your advantage?

Lockley says that trying to adjust your clock even before you take that flight can make a huge difference.

"Think, what are those people doing in that time zone and start doing what they're doing," he says.

If you're going from New York to Los Angeles, you need to delay your system, so go to bed later than normal for several days before your trip. If you're going to London, go to bed earlier.

That's not to say you have to get to bed by 7 p.m. in New York rather than your usual midnight.

Shelby Harris, director of the Behavioral Sleep Medicine Program at New York's Montefiore Medical Center, says adjusting your schedule by just 15 minutes each day in the days leading up to your departure is sufficient. "Even an hour or two can actually make a big difference," she says.

Controlling your exposure to light is also crucial to fighting jet lag, as light is a trigger for your body to wake up.

"The way to think about timing is if you stay up late and see light later, you're delaying your bedtime and delaying your clock," Lockley says. "If we see light early, we wake up early and we're advancing."

Lockley gives a New York-to-London 7 a.m. flight as an example. You arrive at 7 p.m. London time. That's 2 p.m. in New York. You're trying to advance to London time, so you want to see light when you arrive. Stay awake for the next four hours.

If you leave New York at 7 p.m., you arrive in London at 7 a.m., when it's 2 a.m. in New York. You wouldn't want to wake up at 2 a.m. So Lockley advises getting as much sleep as you can on the plane with the use of sunglasses or an eye mask, then getting off the plane and keeping sunglasses on. At 11 a.m. London time, when it's 6 a.m. in New York, you're ready for light.

A typical traveler would try to expose him or herself to light right away to adjust to the new time zone.

"Simplistic advice, which is to get on the new time zone as quickly as you can, is only right half the time," he says.

If you have trouble sleeping, the use of melatonin, a natural sleep-inducer, or a sleeping pill such as Ambien could help, but experts say you should consult your doctor first.

Hackney, who averages about 150 days on the road each year, would rather try a more natural approach. She eats healthy snacks on the flight and limits the amount of alcohol she drinks.

And she tries to sleep as much as she can on the plane with the use of an eye wrap, blanket, travel pillow and noise-canceling headphones. "I would never travel without them," she says.